Breast cancer remains one of the top three cancers to affect and cause mortality in women. Major shortcomings with current treatment are the high level of side effects induced in patients and insufficient efficacy, particularly for patients with metastatic disease. Targeted cancer therapy is designed to treat only the cancer cells and minimize damage to healthy cells. These targets are critical to the tumor's malignant phenotype but not to the host's normal tissues, improving outcomes while minimizing systemic side effects. Anti-HER2, Herceptin, leads the way for targeted therapy in breast cancer with a much lower incidence of side effects and definite efficacy in a specific but small subset of patients. However, there is a clear need for additional therapeutic options including other novel targeted therapies. The 88 kDa autocrine growth factor called PC-Cell Derived Growth Factor (PCDGF), also known as granulin precursor (GP88), has been shown to play a critical role in breast cancer cell biology, exemplified by the following: 1) GP88 is an autocrine growth/survival factor for breast cancer cells, 2) increased GP88 expression in breast cancer cells is associated with increased tumorigenicity, 3) GP88 mediates tumor cell angiogenesis and invasiveness, 4) breast cancer cells overexpressing GP88 are resistant to current therapies - Tamoxifen, Faslodex, doxorubicin, 5) increased GP88 expression in breast cancer tissue correlates with clinical parameters of poor prognosis while normal and benign breast tissue are negative, 6) patients with poor prognosis have elevated GP88 serum levels. These experiments show the essential role that GP88 plays in breast cancer cell tumorigenesis and that the inhibition of GP88 expression or function leads to inhibition of tumor growth. These results highlight the importance of GP88 for targeted therapy of breast cancer via the development of anti-GP88 therapeutic neutralizing monoclonal antibodies (Mabs). Our Phase I research proposed to evaluate a library of murine anti-GP88 for antigen binding properties and for biological activity in GP88-dependent in vitro and in vivo functional tumor cell models. These Phase I specific aims were accomplished and resulted in the identification of anti-GP88 neutralizing Mabs with the in vitro and in vivo potency and efficacy to be candidates for targeted therapy in breast cancer to address a vitally important unmet clinical need. We have selected one Mab, AG1, for further pre-clinical development activities, specifically the generation and characterization of a recombinant Mab (chimerized and humanized Mabs). The following Specific Aims are proposed for this Phase II SBIR application: 1. Cloning of the cDNA encoding the variable sequences of the light chain and heavy chain of the antibody expressed by the AG1 hybridoma cells and generation of expression vectors for both a humanized (HuAG1) and a mouse-human chimeric antibody (ChAG1). 2. Transient expression of the HuAG1 and ChAG1 chimeric antibodies and validation of their binding properties. The antigen binding characteristics and biological activities of the cloned, expressed HuAG1 and ChAG1 will be evaluated and compared with the murine AG1 Mab in order to select candidate recombinant AG1 that fit acceptance criteria for further development. 3. Generate stable HuAG1- or ChAG1-producing cell clones. HuAG1 or ChAG1 selected above will be stably expressed in CHO cells. The HuAG1- or ChAG1-producing clones will be compared for cell growth performance, antibody productivity, and metabolic profile in order to select a candidate clone for scale-up production. 4. Express, purify and characterize the biological properties of the HuAG1 or ChAG1 Mab. The Mab will be evaluated in relevant in vitro and in vivo functional tumor cell models and compared directly with the murine AG1 Mab. GP88 represents a novel, pre-clinically validated target for breast cancer. At the conclusion of this research in this Phase II project, we will have generated a mouse/human chimeric Mab with the in vitro and in vivo pre-clinical efficacy and potency for targeted therapy of breast cancer and we will have developed an optimized clonal antibody production cell line suitable for transfer to a CMO for contract manufacturing. However, once this chimeric anti-GP88 Mab has been generated and characterized it will require further pre-clinical development activities (e.g. formulation, pharmacokinetics and safety) before IND filing for clinical trials in breast cancer. These additional development activities will serve as the basis for a subsequent continuation/renewal Phase II SBIR application. PUBLIC HEALTH RELEVANCE: Breast cancer remains one of the top three cancers to affect and cause mortality in women. Major shortcomings with current treatment are the high level of side effects induced in patients and insufficient efficacy, particularly for patients with advanced disease. The innovative breast cancer therapy to be developed in this proposal will target a mechanism inherent in breast cancer but avoid the side effects associated with many current breast cancer therapies.